Ok, so I’ve just given up on the IDTOOL being even close to accurate. We inflated to the pressures on the door jamb and the light went out. All batteries read OK.
Pressures for the rear wheels now read about 55psi on the IIDTOOL.

 

I'm bringing this back from the dead because I have the same experience and I think no one addressed the real issue. My IID also reports pressures significantly higher than my air pressure gauges. I have seen my IID report all 4 tpms sensors at 14.5psi, and then while driving it will report live values in the 47psi range, about 14.5 psi above what my air pressure gauges show. I have to believe the IID has a function to reset the initial 14.5 reading down to 0.0. Then the IID will report a value in the range of what my air pressure gauges do. Surely someone has enough experience with the IID to walk us though a reset.

 

Just contact GAP, easy as that. They can easily tell you what is doable. I actually had no clue you could read actually pressure with it though, going to look tomorrow. I hate that the LR3 will only say "check pressure all tires". I wish it would say WHICH one.

 

I had an email exchange with Gap Diagnostics back when I was adding to this thread. They felt that the TPMS were not reliable for pressure measurement and could not be calibrated or compensated with software for any accuracy.

 

I believe the gap tool displays absolute pressure, whereas a tire pressure guage is going to display relative pressure above atmosphere. The 14.5 psi displayed initially is atmospheric pressure which they erroneously appear to add to the readout.. So subtract that from the gap tool readout, and you have close to what your pressure guage should read. I guess the guys at gap don't understand tire pressure guages and the spec on the door pillar are relative pressures above atmosphere not absolute pressure. I use my LR3 in Colorado at 10,600ft. So when I inflate my tires to the correct relative pressure 33psi and 42 psi. The absolute pressure is about 4psi lower than at sea level.

 

I'm struggling with an intermittently TPMS light flashing on and off too. All 4 sensors will read 14.5 while driving and then read correctly again. There is no low battery error from any if the sensors, but since the guys who made this tool add an arbitrary 14.5 psi to the readout I'm not sure I trust this tool TPMS testing at all. At tge moment I'm thinking the batteries in all the sensors are near the threshold of transmitting and not transmitting. After they transmit the batteries need time to recover, and miss a few times causing the light to come on. Then they recover and transmit correctly resetting the light. If that is what is happening then the tool should pick up a low battery code from the sensor, but it doesn't appear to.

 

Just FYI, I have a thinktool pad10 and the tpms sensors are reporting the same values as my gap tool which are all much higher than what my gauge shows. It's not just the gap tool.